Question

I have a dynamic Actionscript class as follows:

public dynamic class Foo {....}

In my code I (may) add some properties to it:

myFoo["myNewDynamicProp"] = "bar";

Elsewhere in my code, given an instance of class Foo, how can I determine if that dynamic property has been added already without throwing an expensive exception?

Answer 1

You can do one of three things. First, calling a property that doesn’t exist on a dyanmic instance doesn’t throw an exception. It just returns undefined, so you can just test for that. Or you can use the in keyword. Or you can use the hasOwnProperty() method.

Consider the following:

var myFoo:Foo = new Foo();

myFoo.newProp = "bar";

trace(myFoo.newProp != undefined); // true
trace(myFoo.nothing != undefined); // false

trace("newProp" in myFoo); // true
trace("nothing" in myFoo); // false

trace(myFoo.hasOwnProperty("newProp")); // true
trace(myFoo.hasOwnProperty("nothing")); // false

You could also just as easily use bracket notation for the first example: myFoo['nothing']